Dynamic range control of intermediate data in resampling process

ABSTRACT

An apparatus for coding video information according to certain aspects includes a memory and a processor. The memory unit is configured to store video information. The processor is configured to: obtain reference layer video information; upsample the reference layer video information in a first dimension to generate an intermediate output; constrain the intermediate output to a predetermined bit depth; and upsample the constrained intermediate output in a second dimension, wherein the second dimension is orthogonal to the first dimension.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/832,648, filed Jun. 7, 2013, which is incorporated by reference inits entirety.

BACKGROUND

1. Field

This disclosure is related to the field of video coding and compression.In particular, it is related to scalable video coding (SVC), includingSVC for Advanced Video Coding (AVC), as well as SVC for High EfficiencyVideo Coding (HEVC), which is also referred to as Scalable HEVC (SHVC).It is also related to 3D video coding, such as the multiview extensionof HEVC, referred to as MV-HEVC and 3D-HEVC. Various embodiments relateto systems and methods for dynamic range control of intermediate data inresampling process.

2. Description of the Related Art

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), the High Efficiency Video Coding (HEVC) standard presentlyunder development, and extensions of such standards. The video devicesmay transmit, receive, encode, decode, and/or store digital videoinformation more efficiently by implementing such video codingtechniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video frame or a portion of a video frame) may bepartitioned into video blocks, which may also be referred to astreeblocks, coding units (CUs) and/or coding nodes. Video blocks in anintra-coded (I) slice of a picture are encoded using spatial predictionwith respect to reference samples in neighboring blocks in the samepicture. Video blocks in an inter-coded (P or B) slice of a picture mayuse spatial prediction with respect to reference samples in neighboringblocks in the same picture or temporal prediction with respect toreference samples in other reference pictures. Pictures may be referredto as frames, and reference pictures may be referred to a referenceframes.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. An inter-codedblock is encoded according to a motion vector that points to a block ofreference samples forming the predictive block, and the residual dataindicating the difference between the coded block and the predictiveblock. An intra-coded block is encoded according to an intra-coding modeand the residual data. For further compression, the residual data may betransformed from the pixel domain to a transform domain, resulting inresidual transform coefficients, which then may be quantized. Thequantized transform coefficients, initially arranged in atwo-dimensional array, may be scanned in order to produce aone-dimensional vector of transform coefficients, and entropy coding maybe applied to achieve even more compression.

SUMMARY

In general, this disclosure describes techniques related to scalablevideo coding (SVC). Various techniques described below provide describemethods and devices for dynamic range control of intermediate data inresampling process.

An apparatus for coding video information according to certain aspectsincludes a memory and a processor. The memory unit is configured tostore video information. The processor is configured to: obtainreference layer video information; upsample the reference layer videoinformation in a first dimension to generate an intermediate output;constrain the intermediate output to a predetermined bit depth; andupsample the constrained intermediate output in a second dimension,wherein the second dimension is orthogonal to the first dimension.

The details of one or more examples are set forth in the accompanyingdrawings and the description below, which are not intended to limit thefull scope of the inventive concepts described herein. Other features,objects, and advantages will be apparent from the description anddrawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Throughout the drawings, reference numbers may be re-used to indicatecorrespondence between referenced elements. The drawings are provided toillustrate example embodiments described herein and are not intended tolimit the scope of the disclosure.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may utilize techniques in accordance with aspectsdescribed in this disclosure.

FIG. 2A is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 2B is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3A is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3B is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 4 is a flowchart illustrating an example method for dynamic rangecontrol of intermediate data in resampling process, according to aspectsof this disclosure.

FIG. 5 is a flowchart illustrating another example method for dynamicrange control of intermediate data in resampling process, according toaspects of this disclosure.

DETAILED DESCRIPTION

The techniques described in this disclosure generally relate to scalablevideo coding (SHVC, SVC) and multiview/3D video coding (e.g., multiviewcoding plus depth, MVC+D). For example, the techniques may be relatedto, and used with or within, a High Efficiency Video Coding (HEVC)scalable video coding (SVC, sometimes referred to as SHVC) extension. Inan SHVC, SVC extension, there could be multiple layers of videoinformation. The layer at the lowest level of the video information mayserve as a base layer (BL) or reference layer (RL), and the layer at thevery top (or the highest layer) of the video information may serve as anenhanced layer (EL). The “enhanced layer” is sometimes referred to as an“enhancement layer,” and these terms may be used interchangeably. Thebase layer is sometimes referred to as a “reference layer,” and theseterms may also be used interchangeably. All layers in between the baselayer and the top layer may serve as additional ELs and/or referencelayers. For example, a given layer may be an EL for a layer below (e.g.,that precedes) the given layer, such as the base layer or anyintervening enhancement layer. Further, the given layer may also serveas a RL for one or more the enhancement layer(s) above (e.g., subsequentto) the given layer. Any layer in between the base layer (e.g., thelowest layer having, for example, a layer identification (ID) set orequal to “1”) and the top layer (or the highest layer) may be used as areference for inter-layer prediction by a layer higher to the givenlayer and may use a layer lower to the given layer as a reference forinter-layer prediction. For example, the given layer can be determinedusing a layer lower to the given layer as a reference for inter-layerprediction.

For simplicity, examples are presented in terms of just two layers: a BLand an EL; however, it should be well understood that the ideas andembodiments described below are applicable to cases with multiplelayers, as well. In addition, for ease of explanation, the terms“frames” or “blocks” are often used. However, these terms are not meantto be limiting. For example, the techniques described below can be usedwith any of a variety of video units, including but not limited topixels, blocks (e.g., CU, PU, TU, macroblocks, etc.), slices, frames,picture, etc.

Video Coding

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual andITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its ScalableVideo Coding (SVC) and Multi-view Video Coding (MVC) and Multi-viewCoding plus Depth (MVC+D) extensions. The latest HEVC draftspecification, and referred to as HEVC WD10 hereinafter, is availablefrom http://phenix.int-evey.fr/jct/doc_end_user/documents/12Geneva/wg11/JCTV C-L1003-v34.zip. The multiview extension to HEVC,namely MV-HEVC, is also being developed by the JCT-3V. A recent WorkingDraft (WD) of MV-HEVC WD3 hereinafter, is available fromhttp://phenix.it-sudparis.eu/jct2/doc_end_user/documents/3_Geneva/wg11/JCT3V-C1004-v4.zip.The scalable extension to HEVC, named SHVC, is also being developed bythe JCT-VC. A recent Working Draft (WD) of SHVC and referred to as SHVCWD1 hereinafter, is available fromhttp://phenix.int-evry.fr/jct/doc_end_user/documents/12_Geneva/wg11/JCTVC-L1008-v1.zip.

In SVC and SHVC, video information may be provided as multiple layers.The layer at the very bottom level can just serve as a base layer (BL)and the layer at the very top level can serve as an enhancement layer(EL). All the layers between the top and bottom layers may serve as bothenhancement layers and reference layers. For example, a layer in themiddle can be an EL for the layers below it, and at the same time as aRL for the layers above it. For simplicity of description, we can assumethat there are two layers, a BL and an EL, in illustrating thetechniques described below. However, all the techniques described hereinare applicable to cases with multiple (more than two) layers, as well.

Scalable video coding (SVC) may be used to provide quality (alsoreferred to as signal-to-noise (SNR)) scalability, spatial scalabilityand/or temporal scalability. For example, in one embodiment, a referencelayer (e.g., a base layer) includes video information sufficient todisplay a video at a first quality level and the enhancement layerincludes additional video information relative to the reference layersuch that the reference layer and the enhancement layer together includevideo information sufficient to display the video at a second qualitylevel higher than the first level (e.g., less noise, greater resolution,better frame rate, etc.). An enhanced layer may have different spatialresolution than a base layer. For example, the spatial aspect ratiobetween EL and BL can be 1.0, 1.5, 2.0 or other different ratios. Inother words, the spatial aspect of the EL may equal 1.0, 1.5, or 2.0times the spatial aspect of the BL. In some examples, the scaling factorof the EL may be greater than the BL. For example, a size of pictures inthe EL may be greater than a size of pictures in the BL. In this way, itmay be possible, although not a limitation, that the spatial resolutionof the EL is larger than the spatial resolution of the BL.

In SVC, which refers to the SVC extension for H.264 or the SHVCextension for H.265 (as discussed above), prediction of a current blockmay be performed using the different layers that are provided for SVC.Such prediction may be referred to as inter-layer prediction.Inter-layer prediction methods may be utilized in SVC in order to reduceinter-layer redundancy. Some examples of inter-layer prediction mayinclude inter-layer intra prediction, inter-layer motion prediction, andinter-layer residual prediction. Inter-layer intra prediction uses thereconstruction of co-located blocks in the base layer to predict thecurrent block in the enhancement layer. Inter-layer motion predictionuses motion information (including motion vectors) of the base layer topredict motion in the enhancement layer. Inter-layer residual predictionuses the residue of the base layer to predict the residue of theenhancement layer.

Overview

In SHVC, a reference layer picture may need to be resampled, forexample, for interlayer prediction in the enhancement layer. Theresampling can be performed by applying a resampling filter to lumasamples from the reference layer picture. For example, an n-tap filtercan be applied. The resampling process can occur in two steps fortwo-dimensional resampling. First, horizontal resampling can beperformed, and then, the vertical resampling can be performed. Forexample, vertical resampling can be performed on the video informationoutput from the horizontal resampling process. The resampling filter canreceive luma samples as input, and the horizontal resampling process cangenerate an intermediate output based on the input luma samples. Theintermediate output can then be used as the input for the verticalresampling step. In some situations, the horizontal resampling processmay add additional bits to the input luma samples such that theintermediate output has more bits (e.g., has a greater bit depth) thanthe input luma samples. The additional bits can make the data rangequite large and may have a significant impact on the computationalcomplexity of the vertical resampling step. For example, the buffer forthe intermediate data may be increased proportionately as data rangebecomes higher. Also, the complexity of interpolation process,especially the multiplication operation, can be highly dependent on thebit-depth of the input data. In addition, there are certaincomputational instruction sets that require inputs having a bit depth nogreater than a certain predetermined maximum. For example, certain16-bit instruction sets may only be used on inputs having 16 bits (e.g.,having a 16-bit bit depth). Accordingly, it would be advantageous toconstrain (e.g., reduce or limit) the bit depth of the intermediateoutput of the first stage of a multi-stage resampling process.

In order to address these and other issues, the techniques described inthis disclosure can constrain the bit depth of the intermediate outputfrom an initial resampling process (e.g., horizontal resampling) to aspecified number of bits. In some embodiments, constraining the bitdepth to a specified number of bits can be accomplished by rightshifting (e.g., applying a right shift operation “>>”) the intermediateoutput by a certain number of bits. The number of bits to right shiftthe intermediate output can be determined based on the bit depth of theinput luma samples input to the resampling filter. For example, theintermediate output can be constrained to 16 bits, and the number ofbits to right shift the intermediate output can be calculated bysubtracting 8 bits from the bit depth of the input luma samples. Thenumber of bits shift can be determined dynamically based on the numberof bits of the input luma samples. As mentioned above, additional bitsadded to the intermediate output from the initial resampling process(e.g., horizontal resampling) can make the data range large and have asignificant impact on the computational complexity of the nextresampling process (e.g., vertical resampling). Constraining theintermediate output in this way can mitigate these issues and/orproblems. Moreover, constraining the intermediate output in this way canlead to more accurate results and reduce rounding error, and can allow acoding device and process to take advantage of certain more efficientcoding instruction sets.

In some embodiments, the output from the vertical resampling process canalso be constrained in a similar manner. In certain embodiments, thevertical resampling process can be performed prior to the horizontalresampling process. The techniques can also be applied tothree-dimensional coding. For example, the intermediate output fromresampling in the x-axis can be constrained to a predetermined bitdepth, and the intermediate output from resampling in the y-axis canalso be constrained to a predetermined bit depth. The number of bits toshift by can be based on the bit depth of the input luma samples and/orthe bit depth of the intermediate output from the previous step inresampling. Generally, the reference layer picture is generallyupsampled, but in some embodiments, the enhancement layer picture may bedownsampled.

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to any specific structureor function presented throughout this disclosure. Rather, these aspectsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the disclosure to those skilled in theart. Based on the teachings herein one skilled in the art shouldappreciate that the scope of the disclosure is intended to cover anyaspect of the novel systems, apparatuses, and methods disclosed herein,whether implemented independently of, or combined with, any other aspectof the invention. For example, an apparatus may be implemented or amethod may be practiced using any number of the aspects set forthherein. In addition, the scope of the invention is intended to coversuch an apparatus or method which is practiced using other structure,functionality, or structure and functionality in addition to or otherthan the various aspects of the invention set forth herein. It should beunderstood that any aspect disclosed herein may be embodied by one ormore elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

Video Coding System

FIG. 1 is a block diagram that illustrates an example video codingsystem 10 that may utilize techniques in accordance with aspectsdescribed in this disclosure. As used described herein, the term “videocoder” refers generically to both video encoders and video decoders. Inthis disclosure, the terms “video coding” or “coding” may refergenerically to video encoding and video decoding.

As shown in FIG. 1, video coding system 10 includes a source device 12and a destination device 14. Source device 12 generates encoded videodata. Destination device 14 may decode the encoded video data generatedby source device 12. Source device 12 can provide the video data to thedestination device 14 via a communication channel 16, which may includea computer-readable storage medium or other communication channel.Source device 12 and destination device 14 may include a wide range ofdevices, including desktop computers, notebook (e.g., laptop) computers,tablet computers, set-top boxes, telephone handsets, such as so-called“smart” phones, so-called “smart” pads, televisions, cameras, displaydevices, digital media players, video gaming consoles, in-car computers,video streaming devices, or the like. Source device 12 and destinationdevice 14 may be equipped for wireless communication.

Destination device 14 may receive the encoded video data to be decodedvia communication channel 16. Communication channel 16 may comprise atype of medium or device capable of moving the encoded video data fromsource device 12 to destination device 14. For example, communicationchannel 16 may comprise a communication medium to enable source device12 to transmit encoded video data directly to destination device 14 inreal-time. The encoded video data may be modulated according to acommunication standard, such as a wireless communication protocol, andtransmitted to destination device 14. The communication medium maycomprise a wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network, such asthe Internet. The communication medium may include routers, switches,base stations, or other equipment that may be useful to facilitatecommunication from source device 12 to destination device 14.

In some embodiments, encoded data may be output from output interface 22to a storage device. In such examples, channel 16 may correspond to astorage device or computer-readable storage medium that stores theencoded video data generated by source device 12. For example,destination device 14 may access the computer-readable storage mediumvia disk access or card access. Similarly, encoded data may be accessedfrom the computer-readable storage medium by input interface 28. Thecomputer-readable storage medium may include any of a variety ofdistributed or locally accessed data storage media such as a hard drive,Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatilememory, or other digital storage media for storing video data. Thecomputer-readable storage medium may correspond to a file server oranother intermediate storage device that may store the encoded videogenerated by source device 12. Destination device 14 may access storedvideo data from the computer-readable storage medium via streaming ordownload. The file server may be a type of server capable of storingencoded video data and transmitting that encoded video data to thedestination device 14. Example file servers include a web server (e.g.,for a website), an FTP server, network attached storage (NAS) devices,or a local disk drive. Destination device 14 may access the encodedvideo data through a standard data connection, including an Internetconnection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., DSL, cable modem, etc.), or acombination of both that is suitable for accessing encoded video datastored on a file server. The transmission of encoded video data from thecomputer-readable storage medium may be a streaming transmission, adownload transmission, or a combination of both.

The techniques of this disclosure can apply applications or settings inaddition to wireless applications or settings. The techniques may beapplied to video coding in support of a of a variety of multimediaapplications, such as over-the-air television broadcasts, cabletelevision transmissions, satellite television transmissions, Internetstreaming video transmissions, such as dynamic adaptive streaming overHTTP (DASH), digital video that is encoded onto a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some embodiments, system 10 may be configured tosupport one-way or two-way video transmission to support applicationssuch as video streaming, video playback, video broadcasting, and/orvideo telephony.

In FIG. 1, source device 12 includes video source 18, video encoder 20,and output interface 22. Destination device 14 includes input interface28, video decoder 30, and display device 32. Video encoder 20 of sourcedevice 12 may be configured to apply the techniques for coding abitstream including video data conforming to multiple standards orstandard extensions. In other embodiments, a source device and adestination device may include other components or arrangements. Forexample, source device 12 may receive video data from an external videosource 18, such as an external camera. Likewise, destination device 14may interface with an external display device, rather than including anintegrated display device.

Video source 18 of source device 12 may include a video capture device,such as a video camera, a video archive containing previously capturedvideo, and/or a video feed interface to receive video from a videocontent provider. Video source 18 may generate computer graphics-baseddata as the source video, or a combination of live video, archivedvideo, and computer-generated video. In some embodiments, if videosource 18 is a video camera, source device 12 and destination device 14may form so-called camera phones or video phones. The captured,pre-captured, or computer-generated video may be encoded by videoencoder 20. The encoded video information may be output by outputinterface 22 to a communication channel 16, which may include acomputer-readable storage medium, as discussed above.

Computer-readable storage medium may include transient media, such as awireless broadcast or wired network transmission, or storage media(e.g., non-transitory storage media), such as a hard disk, flash drive,compact disc, digital video disc, Blu-ray disc, or othercomputer-readable media. A network server (not shown) may receiveencoded video data from source device 12 and provide the encoded videodata to destination device 14 (e.g., via network transmission). Acomputing device of a medium production facility, such as a discstamping facility, may receive encoded video data from source device 12and produce a disc containing the encoded video data. Therefore,communication channel 16 may be understood to include one or morecomputer-readable storage media of various forms.

Input interface 28 of destination device 14 can receive information fromcommunication channel 16. The information of communication channel 16may include syntax information defined by video encoder 20, which can beused by video decoder 30, that includes syntax elements that describecharacteristics and/or processing of blocks and other coded units, e.g.,GOPs. Display device 32 displays the decoded video data to a user, andmay include any of a variety of display devices such as a cathode raytube (CRT), a liquid crystal display (LCD), a plasma display, an organiclight emitting diode (OLED) display, or another type of display device.

Video encoder 20 and video decoder 30 may operate according to a videocoding standard, such as the High Efficiency Video Coding (HEVC)standard presently under development, and may conform to the HEVC TestModel (HM). Alternatively, video encoder 20 and video decoder 30 mayoperate according to other proprietary or industry standards, such asthe ITU-T H.264 standard, alternatively referred to as MPEG-4, Part 10,Advanced Video Coding (AVC), or extensions of such standards. Thetechniques of this disclosure, however, are not limited to anyparticular coding standard. Other examples of video coding standardsinclude MPEG-2 and ITU-T H.263. Although not shown in FIG. 1, in someaspects, video encoder 20 and video decoder 30 may each be integratedwith an audio encoder and decoder, and may include appropriate MUX-DEMUXunits, or other hardware and software, to handle encoding of both audioand video in a common data stream or separate data streams. Ifapplicable, MUX-DEMUX units may conform to the ITU H.223 multiplexerprotocol, or other protocols such as the user datagram protocol (UDP).

FIG. 1 is merely an example and the techniques of this disclosure mayapply to video coding settings (e.g., video encoding or video decoding)that do not necessarily include any data communication between theencoding and decoding devices. In other examples, data can be retrievedfrom a local memory, streamed over a network, or the like. An encodingdevice may encode and store data to memory, and/or a decoding device mayretrieve and decode data from memory. In many examples, the encoding anddecoding is performed by devices that do not communicate with oneanother, but simply encode data to memory and/or retrieve and decodedata from memory.

Video encoder 20 and video decoder 30 each may be implemented as any ofa variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a non-transitorycomputer-readable medium and execute the instructions in hardware usingone or more processors to perform the techniques of this disclosure.Each of video encoder 20 and video decoder 30 may be included in one ormore encoders or decoders, either of which may be integrated as part ofa combined encoder/decoder (CODEC) in a respective device. A deviceincluding video encoder 20 and/or video decoder 30 may comprise anintegrated circuit, a microprocessor, and/or a wireless communicationdevice, such as a cellular telephone.

The JCT-VC is working on development of the HEVC standard and itsextension and Version 1 has been finalized. The HEVC standardizationefforts are based on an evolving model of a video coding device referredto as the HEVC Test Model (HM). The HM presumes several additionalcapabilities of video coding devices relative to existing devicesaccording to, e.g., ITU-T H.264/AVC. For example, whereas H.264 providesnine intra-prediction encoding modes, the HM may provide as many asthirty-three intra-prediction encoding modes.

In general, the working model of the HM describes that a video frame orpicture may be divided into a sequence of treeblocks or largest codingunits (LCU) that include both luma and chroma samples. Syntax datawithin a bitstream may define a size for the LCU, which is a largestcoding unit in terms of the number of pixels. A slice includes a numberof consecutive treeblocks in coding order. A video frame or picture maybe partitioned into one or more slices. Each treeblock may be split intocoding units (CUs) according to a quadtree. In general, a quadtree datastructure includes one node per CU, with a root node corresponding tothe treeblock. If a CU is split into four sub-CUs, the nodecorresponding to the CU includes four leaf nodes, each of whichcorresponds to one of the sub-CUs.

Each node of the quadtree data structure may provide syntax data for thecorresponding CU. For example, a node in the quadtree may include asplit flag, indicating whether the CU corresponding to the node is splitinto sub-CUs. Syntax elements for a CU may be defined recursively, andmay depend on whether the CU is split into sub-CUs. If a CU is not splitfurther, it is referred as a leaf-CU. In this disclosure, four sub-CUsof a leaf-CU will also be referred to as leaf-CUs even if there is noexplicit splitting of the original leaf-CU. For example, if a CU at16×16 size is not split further, the four 8×8 sub-CUs will also bereferred to as leaf-CUs although the 16×16 CU was never split.

A CU has a similar purpose as a macroblock of the H.264 standard, exceptthat a CU does not have a size distinction. For example, a treeblock maybe split into four child nodes (also referred to as sub-CUs), and eachchild node may in turn be a parent node and be split into another fourchild nodes. A final, unsplit child node, referred to as a leaf node ofthe quadtree, comprises a coding node, also referred to as a leaf-CU.Syntax data associated with a coded bitstream may define a maximumnumber of times a treeblock may be split, referred to as a maximum CUdepth, and may also define a minimum size of the coding nodes.Accordingly, a bitstream may also define a smallest coding unit (SCU).This disclosure uses the term “block” to refer to any of a CU, PU, orTU, in the context of HEVC, or similar data structures in the context ofother standards (e.g., macroblocks and sub-blocks thereof in H.264/AVC).

A CU includes a coding node and prediction units (PUs) and transformunits (TUs) associated with the coding node. A size of the CUcorresponds to a size of the coding node and must be square in shape.The size of the CU may range from 8×8 pixels up to the size of thetreeblock with a maximum of 64×64 pixels or greater. Each CU may containone or more PUs and one or more TUs. Syntax data associated with a CUmay describe, for example, partitioning of the CU into one or more PUs.Partitioning modes may differ between whether the CU is skip or directmode encoded, intra-prediction mode encoded, or inter-prediction modeencoded. PUs may be partitioned to be non-square in shape. Syntax dataassociated with a CU may also describe, for example, partitioning of theCU into one or more TUs according to a quadtree. A TU can be square ornon-square (e.g., rectangular) in shape.

The HEVC standard allows for transformations according to TUs, which maybe different for different CUs. The TUs are typically sized based on thesize of PUs within a given CU defined for a partitioned LCU, althoughthis may not always be the case. The TUs are typically the same size orsmaller than the PUs. In some examples, residual samples correspondingto a CU may be subdivided into smaller units using a quadtree structureknown as “residual quad tree” (RQT). The leaf nodes of the RQT may bereferred to as transform units (TUs). Pixel difference values associatedwith the TUs may be transformed to produce transform coefficients, whichmay be quantized.

A leaf-CU may include one or more prediction units (PUs). In general, aPU represents a spatial area corresponding to all or a portion of thecorresponding CU, and may include data for retrieving a reference samplefor the PU. Moreover, a PU includes data related to prediction. Forexample, when the PU is intra-mode encoded, data for the PU may beincluded in a residual quadtree (RQT), which may include data describingan intra-prediction mode for a TU corresponding to the PU. As anotherexample, when the PU is inter-mode encoded, the PU may include datadefining one or more motion vectors for the PU. The data defining themotion vector for a PU may describe, for example, a horizontal componentof the motion vector, a vertical component of the motion vector, aresolution for the motion vector (e.g., one-quarter pixel precision orone-eighth pixel precision), a reference picture to which the motionvector points, and/or a reference picture list (e.g., List 0, List 1, orList C) for the motion vector.

A leaf-CU having one or more PUs may also include one or more transformunits (TUs). The transform units may be specified using an RQT (alsoreferred to as a TU quadtree structure), as discussed above. Forexample, a split flag may indicate whether a leaf-CU is split into fourtransform units. Then, each transform unit may be split further intofurther sub-TUs. When a TU is not split further, it may be referred toas a leaf-TU. Generally, for intra coding, all the leaf-TUs belonging toa leaf-CU share the same intra prediction mode. That is, the sameintra-prediction mode is generally applied to calculate predicted valuesfor all TUs of a leaf-CU. For intra coding, a video encoder maycalculate a residual value for each leaf-TU using the intra predictionmode, as a difference between the portion of the CU corresponding to theTU and the original block. A TU is not necessarily limited to the sizeof a PU. Thus, TUs may be larger or smaller than a PU. For intra coding,a PU may be collocated with a corresponding leaf-TU for the same CU. Insome examples, the maximum size of a leaf-TU may correspond to the sizeof the corresponding leaf-CU.

Moreover, TUs of leaf-CUs may also be associated with respectivequadtree data structures, referred to as residual quadtrees (RQTs). Thatis, a leaf-CU may include a quadtree indicating how the leaf-CU ispartitioned into TUs. The root node of a TU quadtree generallycorresponds to a leaf-CU, while the root node of a CU quadtree generallycorresponds to a treeblock (or LCU). TUs of the RQT that are not splitare referred to as leaf-TUs. In general, this disclosure uses the termsCU and TU to refer to leaf-CU and leaf-TU, respectively, unless notedotherwise.

A video sequence typically includes a series of video frames orpictures. A group of pictures (GOP) generally comprises a series of oneor more of the video pictures. A GOP may include syntax data in a headerof the GOP, a header of one or more of the pictures, or elsewhere, thatdescribes a number of pictures included in the GOP. Each slice of apicture may include slice syntax data that describes an encoding modefor the respective slice. Video encoder 20 typically operates on videoblocks within individual video slices in order to encode the video data.A video block may correspond to a coding node within a CU. The videoblocks may have fixed or varying sizes, and may differ in size accordingto a specified coding standard.

As an example, the HM supports prediction in various PU sizes. Assumingthat the size of a particular CU is 2N×2N, the HM supportsintra-prediction in PU sizes of 2N×2N or N×N, and inter-prediction insymmetric PU sizes of 2N×2N, 2N×N, N×2N, or N×N. The HM also supportsasymmetric partitioning for inter-prediction in PU sizes of 2N×nU,2N×nD, nL×2N, and nR×2N. In asymmetric partitioning, one direction of aCU is not partitioned, while the other direction is partitioned into 25%and 75%. The portion of the CU corresponding to the 25% partition isindicated by an “n” followed by an indication of “Up”, “Down,” “Left,”or “Right.” Thus, for example, “2N×nU” refers to a 2N×2N CU that ispartitioned horizontally with a 2N×0.5N PU on top and a 2N×1.5N PU onbottom.

In this disclosure, “N×N” and “N by N” may be used interchangeably torefer to the pixel dimensions of a video block in terms of vertical andhorizontal dimensions, e.g., 16×16 pixels or 16 by 16 pixels. Ingeneral, a 16×16 block will have 16 pixels in a vertical direction(y=16) and 16 pixels in a horizontal direction (x=16). Likewise, an N×Nblock generally has N pixels in a vertical direction and N pixels in ahorizontal direction, where N represents a nonnegative integer value.The pixels in a block may be arranged in rows and columns. Moreover,blocks need not necessarily have the same number of pixels in thehorizontal direction as in the vertical direction. For example, blocksmay comprise N×M pixels, where M is not necessarily equal to N.

Following intra-predictive or inter-predictive coding using the PUs of aCU, video encoder 20 may calculate residual data for the TUs of the CU.The PUs may comprise syntax data describing a method or mode ofgenerating predictive pixel data in the spatial domain (also referred toas the pixel domain) and the TUs may comprise coefficients in thetransform domain following application of a transform, e.g., a discretesine transform (DST), a discrete cosine transform (DCT), an integertransform, a wavelet transform, or a conceptually similar transform toresidual video data. The residual data may correspond to pixeldifferences between pixels of the unencoded picture and predictionvalues corresponding to the PUs. Video encoder 20 may form the TUsincluding the residual data for the CU, and then transform the TUs toproduce transform coefficients for the CU.

Following any transforms to produce transform coefficients, videoencoder 20 may perform quantization of the transform coefficients.Quantization is a broad term intended to have its broadest ordinarymeaning. In one embodiment, quantization refers to a process in whichtransform coefficients are quantized to possibly reduce the amount ofdata used to represent the coefficients, providing further compression.The quantization process may reduce the bit depth associated with someor all of the coefficients. For example, an n-bit value may be roundeddown to an m-bit value during quantization, where n is greater than m.

Following quantization, the video encoder may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) coefficients at the front of the array and to place lowerenergy (and therefore higher frequency) coefficients at the back of thearray. In some examples, video encoder 20 may utilize a predefined scanorder to scan the quantized transform coefficients to produce aserialized vector that can be entropy encoded. In other examples, videoencoder 20 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form a one-dimensional vector, video encoder20 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive variable length coding (CAVLC), context-adaptive binaryarithmetic coding (CABAC), syntax-based context-adaptive binaryarithmetic coding (SBAC), Probability Interval Partitioning Entropy(PIPE) coding or another entropy encoding methodology. Video encoder 20may also entropy encode syntax elements associated with the encodedvideo data for use by video decoder 30 in decoding the video data.

To perform CABAC, video encoder 20 may assign a context within a contextmodel to a symbol to be transmitted. The context may relate to, forexample, whether neighboring values of the symbol are non-zero or not.To perform CAVLC, video encoder 20 may select a variable length code fora symbol to be transmitted. Codewords in VLC may be constructed suchthat relatively shorter codes correspond to more probable symbols, whilelonger codes correspond to less probable symbols. In this way, the useof VLC may achieve a bit savings over, for example, using equal-lengthcodewords for each symbol to be transmitted. The probabilitydetermination may be based on a context assigned to the symbol.

Video encoder 20 may further send syntax data, such as block-basedsyntax data, frame-based syntax data, and GOP-based syntax data, tovideo decoder 30, e.g., in a frame header, a block header, a sliceheader, or a GOP header. The GOP syntax data may describe a number offrames in the respective GOP, and the frame syntax data may indicate anencoding/prediction mode used to encode the corresponding frame.

Video Encoder

FIG. 2A is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure. Video encoder 20 may be configured to process a singlelayer of a video bitstream, such as for HEVC. Further, video encoder 20may be configured to perform any or all of the techniques of thisdisclosure, including but not limited to the methods for dynamic rangecontrol of intermediate data in resampling process and related processesdescribed in greater detail above and below with respect to FIGS. 4-5.As one example, inter-layer prediction unit 66 (when provided) may beconfigured to perform any or all of the techniques described in thisdisclosure. However, aspects of this disclosure are not so limited. Insome examples, the techniques described in this disclosure may be sharedamong the various components of video encoder 20. In some examples,additionally or alternatively, a processor (not shown) may be configuredto perform any or all of the techniques described in this disclosure.

For purposes of explanation, this disclosure describes video encoder 20in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Theencoder 20 of FIG. 2A illustrates a single layer of a codec. However, aswill be described further with respect to FIG. 2B, some or all of thevideo encoder 20 may be duplicated for processing according to amulti-layer codec.

Video encoder 20 may perform intra-, inter-, and inter-layer prediction(sometime referred to as intra-, inter- or inter-layer coding) of videoblocks within video slices. Intra coding relies on spatial prediction toreduce or remove spatial redundancy in video within a given video frameor picture. Inter-coding relies on temporal prediction to reduce orremove temporal redundancy in video within adjacent frames or picturesof a video sequence. Inter-layer coding relies on prediction based uponvideo within a different layer(s) within the same video coding sequence.Intra-mode (I mode) may refer to any of several spatial based codingmodes. Inter-modes, such as uni-directional prediction (P mode) orbi-prediction (B mode), may refer to any of several temporal-basedcoding modes.

As shown in FIG. 2A, video encoder 20 receives a current video blockwithin a video frame to be encoded. In the example of FIG. 2A, videoencoder 20 includes mode select unit 40, reference frame memory 64,summer 50, transform processing unit 52, quantization unit 54, andentropy encoding unit 56. Mode select unit 40, in turn, includes motioncompensation unit 44, motion estimation unit 42, intra-prediction unit46, inter-layer prediction unit 66, and partition unit 48. Referenceframe memory 64 may include a decoded picture buffer. The decodedpicture buffer is a broad term having its ordinary meaning, and in someembodiments refers to a video codec-managed data structure of referenceframes.

For video block reconstruction, video encoder 20 also includes inversequantization unit 58, inverse transform unit 60, and summer 62. Adeblocking filter (not shown in FIG. 2A) may also be included to filterblock boundaries to remove blockiness artifacts from reconstructedvideo. If desired, the deblocking filter would typically filter theoutput of summer 62. Additional filters (in loop or post loop) may alsobe used in addition to the deblocking filter. Such filters are not shownfor brevity, but if desired, may filter the output of summer 50 (as anin-loop filter).

During the encoding process, video encoder 20 receives a video frame orslice to be coded. The frame or slice may be divided into multiple videoblocks. Motion estimation unit 42 and motion compensation unit 44perform inter-predictive coding of the received video block relative toone or more blocks in one or more reference frames to provide temporalprediction. Intra-prediction unit 46 may alternatively performintra-predictive coding of the received video block relative to one ormore neighboring blocks in the same frame or slice as the block to becoded to provide spatial prediction. Video encoder 20 may performmultiple coding passes, e.g., to select an appropriate coding mode foreach block of video data.

Moreover, partition unit 48 may partition blocks of video data intosub-blocks, based on evaluation of previous partitioning schemes inprevious coding passes. For example, partition unit 48 may initiallypartition a frame or slice into LCUs, and partition each of the LCUsinto sub-CUs based on rate-distortion analysis (e.g., rate-distortionoptimization, etc.). Mode select unit 40 may further produce a quadtreedata structure indicative of partitioning of an LCU into sub-CUs.Leaf-node CUs of the quadtree may include one or more PUs and one ormore TUs.

Mode select unit 40 may select one of the coding modes, intra, inter, orinter-layer prediction mode, e.g., based on error results, and providethe resulting intra-, inter-, or inter-layer coded block to summer 50 togenerate residual block data and to summer 62 to reconstruct the encodedblock for use as a reference frame. Mode select unit 40 also providessyntax elements, such as motion vectors, intra-mode indicators,partition information, and other such syntax information, to entropyencoding unit 56.

Motion estimation unit 42 and motion compensation unit 44 may be highlyintegrated, but are illustrated separately for conceptual purposes.Motion estimation, performed by motion estimation unit 42, is theprocess of generating motion vectors, which estimate motion for videoblocks. A motion vector, for example, may indicate the displacement of aPU of a video block within a current video frame or picture relative toa predictive block within a reference frame (or other coded unit)relative to the current block being coded within the current frame (orother coded unit). A predictive block is a block that is found toclosely match the block to be coded, in terms of pixel difference, whichmay be determined by sum of absolute difference (SAD), sum of squaredifference (SSD), or other difference metrics. In some examples, videoencoder 20 may calculate values for sub-integer pixel positions ofreference pictures stored in reference frame memory 64. For example,video encoder 20 may interpolate values of one-quarter pixel positions,one-eighth pixel positions, or other fractional pixel positions of thereference picture. Therefore, motion estimation unit 42 may perform amotion search relative to the full pixel positions and fractional pixelpositions and output a motion vector with fractional pixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a videoblock in an inter-coded slice by comparing the position of the PU to theposition of a predictive block of a reference picture. The referencepicture may be selected from a first reference picture list (List 0) ora second reference picture list (List 1), each of which identify one ormore reference pictures stored in reference frame memory 64. Motionestimation unit 42 sends the calculated motion vector to entropyencoding unit 56 and motion compensation unit 44.

Motion compensation, performed by motion compensation unit 44, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation unit 42. Motion estimation unit42 and motion compensation unit 44 may be functionally integrated, insome examples. Upon receiving the motion vector for the PU of thecurrent video block, motion compensation unit 44 may locate thepredictive block to which the motion vector points in one of thereference picture lists. Summer 50 forms a residual video block bysubtracting pixel values of the predictive block from the pixel valuesof the current video block being coded, forming pixel difference values,as discussed below. In some embodiments, motion estimation unit 42 canperform motion estimation relative to luma components, and motioncompensation unit 44 can use motion vectors calculated based on the lumacomponents for both chroma components and luma components. Mode selectunit 40 may generate syntax elements associated with the video blocksand the video slice for use by video decoder 30 in decoding the videoblocks of the video slice.

Intra-prediction unit 46 may intra-predict or calculate a current block,as an alternative to the inter-prediction performed by motion estimationunit 42 and motion compensation unit 44, as described above. Inparticular, intra-prediction unit 46 may determine an intra-predictionmode to use to encode a current block. In some examples,intra-prediction unit 46 may encode a current block using variousintra-prediction modes, e.g., during separate encoding passes, andintra-prediction unit 46 (or mode select unit 40, in some examples) mayselect an appropriate intra-prediction mode to use from the testedmodes.

For example, intra-prediction unit 46 may calculate rate-distortionvalues using a rate-distortion analysis for the various testedintra-prediction modes, and select the intra-prediction mode having thebest rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original, unencoded blockthat was encoded to produce the encoded block, as well as a bitrate(that is, a number of bits) used to produce the encoded block.Intra-prediction unit 46 may calculate ratios from the distortions andrates for the various encoded blocks to determine which intra-predictionmode exhibits the best rate-distortion value for the block.

After selecting an intra-prediction mode for a block, intra-predictionunit 46 may provide information indicative of the selectedintra-prediction mode for the block to entropy encoding unit 56. Entropyencoding unit 56 may encode the information indicating the selectedintra-prediction mode. Video encoder 20 may include in the transmittedbitstream configuration data, which may include a plurality ofintra-prediction mode index tables and a plurality of modifiedintra-prediction mode index tables (also referred to as codeword mappingtables), definitions of encoding contexts for various blocks, andindications of a most probable intra-prediction mode, anintra-prediction mode index table, and a modified intra-prediction modeindex table to use for each of the contexts.

The video encoder 20 may include an inter-layer prediction unit 66.Inter-layer prediction unit 66 is configured to predict a current block(e.g., a current block in the EL) using one or more different layersthat are available in SVC (e.g., a base or reference layer). Suchprediction may be referred to as inter-layer prediction. Inter-layerprediction unit 66 utilizes prediction methods to reduce inter-layerredundancy, thereby improving coding efficiency and reducingcomputational resource requirements. Some examples of inter-layerprediction include inter-layer intra prediction, inter-layer motionprediction, and inter-layer residual prediction. Inter-layer intraprediction uses the reconstruction of co-located blocks in the baselayer to predict the current block in the enhancement layer. Inter-layermotion prediction uses motion information of the base layer to predictmotion in the enhancement layer. Inter-layer residual prediction usesthe residue of the base layer to predict the residue of the enhancementlayer. When the base and enhancement layers have different spatialresolutions, spatial motion vector scaling and/or inter-layer positionmapping using a temporal scaling function may be performed by theinter-layer prediction unit 66, as described in greater detail below.

Video encoder 20 forms a residual video block by subtracting theprediction data from mode select unit 40 from the original video blockbeing coded. Summer 50 represents the component or components thatperform this subtraction operation. Transform processing unit 52 appliesa transform, such as a discrete cosine transform (DCT) or a conceptuallysimilar transform, to the residual block, producing a video blockcomprising residual transform coefficient values. Transform processingunit 52 may perform other transforms which are conceptually similar toDCT. For example, discrete sine transforms (DST), wavelet transforms,integer transforms, sub-band transforms or other types of transforms canalso be used.

Transform processing unit 52 can apply the transform to the residualblock, producing a block of residual transform coefficients. Thetransform may convert the residual information from a pixel value domainto a transform domain, such as a frequency domain. Transform processingunit 52 may send the resulting transform coefficients to quantizationunit 54. Quantization unit 54 quantizes the transform coefficients tofurther reduce bit rate. The quantization process may reduce the bitdepth associated with some or all of the coefficients. The degree ofquantization may be modified by adjusting a quantization parameter. Insome examples, quantization unit 54 may then perform a scan of thematrix including the quantized transform coefficients. Alternatively,entropy encoding unit 56 may perform the scan.

Following quantization, entropy encoding unit 56 entropy encodes thequantized transform coefficients. For example, entropy encoding unit 56may perform context adaptive variable length coding (CAVLC), contextadaptive binary arithmetic coding (CABAC), syntax-based context-adaptivebinary arithmetic coding (SBAC), probability interval partitioningentropy (PIPE) coding or another entropy coding technique. In the caseof context-based entropy coding, context may be based on neighboringblocks. Following the entropy coding by entropy encoding unit 56, theencoded bitstream may be transmitted to another device (e.g., videodecoder 30) or archived for later transmission or retrieval.

Inverse quantization unit 58 and inverse transform unit 60 apply inversequantization and inverse transformation, respectively, to reconstructthe residual block in the pixel domain (e.g., for later use as areference block). Motion compensation unit 44 may calculate a referenceblock by adding the residual block to a predictive block of one of theframes of reference frame memory 64. Motion compensation unit 44 mayalso apply one or more interpolation filters to the reconstructedresidual block to calculate sub-integer pixel values for use in motionestimation. Summer 62 adds the reconstructed residual block to themotion compensated prediction block produced by motion compensation unit44 to produce a reconstructed video block for storage in reference framememory 64. The reconstructed video block may be used by motionestimation unit 42 and motion compensation unit 44 as a reference blockto inter-code a block in a subsequent video frame.

Multi-Layer Video Encoder

FIG. 2B is a block diagram illustrating an example of a multi-layervideo encoder 21 that may implement techniques in accordance withaspects described in this disclosure. The video encoder 21 may beconfigured to process multi-layer video frames, such as for SHVC andmultiview coding. Further, the video encoder 21 may be configured toperform any or all of the techniques of this disclosure.

The video encoder 21 includes a video encoder 20A and video encoder 20B,each of which may be configured as the video encoder 20 of FIG. 2A andmay perform the functions described above with respect to the videoencoder 20. Further, as indicated by the reuse of reference numbers, thevideo encoders 20A and 20B may include at least some of the systems andsubsystems as the video encoder 20. Although the video encoder 21 isillustrated as including two video encoders 20A and 20B, the videoencoder 21 is not limited as such and may include any number of videoencoder 20 layers. In some embodiments, the video encoder 21 may includea video encoder 20 for each picture or frame in an access unit. Forexample, an access unit that includes five pictures may be processed orencoded by a video encoder that includes five encoder layers. In someembodiments, the video encoder 21 may include more encoder layers thanframes in an access unit. In some such cases, some of the video encoderlayers may be inactive when processing some access units.

In addition to the video encoders 20A and 20B, the video encoder 21 mayinclude a resampling unit 90. The resampling unit 90 may, in some cases,upsample a base layer of a received video frame to, for example, createan enhancement layer. The resampling unit 90 may upsample particularinformation associated with the received base layer of a frame, but notother information. For example, the resampling unit 90 may upsample thespatial size or number of pixels of the base layer, but the number ofslices or the picture order count may remain constant. In some cases,the resampling unit 90 may not process the received video and/or may beoptional. For example, in some cases, the mode select unit 40 mayperform upsampling. In some embodiments, the resampling unit 90 isconfigured to upsample a layer and reorganize, redefine, modify, oradjust one or more slices to comply with a set of slice boundary rulesand/or raster scan rules. Although primarily described as upsampling abase layer, or a lower layer in an access unit, in some cases, theresampling unit 90 may downsample a layer. For example, if duringstreaming of a video bandwidth is reduced, a frame may be downsampledinstead of upsampled. Resampling unit 90 may be further configured toperform cropping and/or padding operations, as well.

The resampling unit 90 may be configured to receive a picture or frame(or picture information associated with the picture) from the decodedpicture buffer 114 of the lower layer encoder (e.g., the video encoder20A) and to upsample the picture (or the received picture information).This upsampled picture may then be provided to the mode select unit 40of a higher layer encoder (e.g., the video encoder 20B) configured toencode a picture in the same access unit as the lower layer encoder. Insome cases, the higher layer encoder is one layer removed from the lowerlayer encoder. In other cases, there may be one or more higher layerencoders between the layer 0 video encoder and the layer 1 encoder ofFIG. 2B.

In some cases, the resampling unit 90 may be omitted or bypassed. Insuch cases, the picture from the decoded picture buffer 64 of the videoencoder 20A may be provided directly, or at least without being providedto the resampling unit 90, to the mode select unit 40 of the videoencoder 20B. For example, if video data provided to the video encoder20B and the reference picture from the decoded picture buffer 64 of thevideo encoder 20A are of the same size or resolution, the referencepicture may be provided to the video encoder 20B without any resampling.

In some embodiments, the video encoder 21 downsamples video data to beprovided to the lower layer encoder using the downsampling unit 94before provided the video data to the video encoder 20A. Alternatively,the downsampling unit 94 may be a resampling unit 90 capable ofupsampling or downsampling the video data. In yet other embodiments, thedownsampling unit 94 may be omitted.

As illustrated in FIG. 2B, the video encoder 21 may further include amultiplexor 98, or mux. The mux 98 can output a combined bitstream fromthe video encoder 21. The combined bitstream may be created by taking abitstream from each of the video encoders 20A and 20B and alternatingwhich bitstream is output at a given time. While in some cases the bitsfrom the two (or more in the case of more than two video encoder layers)bitstreams may be alternated one bit at a time, in many cases thebitstreams are combined differently. For example, the output bitstreammay be created by alternating the selected bitstream one block at atime. In another example, the output bitstream may be created byoutputting a non-1:1 ratio of blocks from each of the video encoders 20Aand 20B. For instance, two blocks may be output from the video encoder20B for each block output from the video encoder 20A. In someembodiments, the output stream from the mux 98 may be preprogrammed. Inother embodiments, the mux 98 may combine the bitstreams from the videoencoders 20A, 20B based on a control signal received from a systemexternal to the video encoder 21, such as from a processor on the sourcedevice 12. The control signal may be generated based on the resolutionor bitrate of a video from the video source 18, based on a bandwidth ofthe channel 16, based on a subscription associated with a user (e.g., apaid subscription versus a free subscription), or based on any otherfactor for determining a resolution output desired from the videoencoder 21.

Video Decoder

FIG. 3A is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure. The video decoder 30 may be configured to process asingle layer of a video bitstream, such as for HEVC. Further, videodecoder 30 may be configured to perform any or all of the techniques ofthis disclosure, including but not limited to the methods for dynamicrange control of intermediate data in resampling process and relatedprocesses described in greater detail above and below with respect toFIGS. 4-5. As one example, inter-layer prediction unit 75 may beconfigured to perform any or all of the techniques described in thisdisclosure. However, aspects of this disclosure are not so limited. Insome examples, the techniques described in this disclosure may be sharedamong the various components of video decoder 30. In some examples,additionally or alternatively, a processor (not shown) may be configuredto perform any or all of the techniques described in this disclosure.

For purposes of explanation, this disclosure describes video decoder 30in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Thedecoder 30 of FIG. 3A illustrates a single layer of a codec. However, aswill be described further with respect to FIG. 3B, some or all of thevideo decoder 30 may be duplicated for processing according to amulti-layer codec.

In the example of FIG. 3A, video decoder 30 includes an entropy decodingunit 70, motion compensation unit 72, intra prediction unit 74,inter-layer prediction unit 75, inverse quantization unit 76, inversetransformation unit 78, reference frame memory 82 and summer 80. In someembodiments, motion compensation unit 72 and/or intra prediction unit 74may be configured to perform inter-layer prediction, in which case theinter-layer prediction unit 75 may be omitted. Video decoder 30 may, insome examples, perform a decoding pass generally reciprocal to theencoding pass described with respect to video encoder 20 (FIG. 2A).Motion compensation unit 72 may generate prediction data based on motionvectors received from entropy decoding unit 70, while intra-predictionunit 74 may generate prediction data based on intra-prediction modeindicators received from entropy decoding unit 70. Reference framememory 82 may include a decoded picture buffer. The decoded picturebuffer is a broad term having its ordinary meaning, and in someembodiments refers to a video codec-managed data structure of referenceframes.

During the decoding process, video decoder 30 receives an encoded videobitstream that represents video blocks of an encoded video slice andassociated syntax elements from video encoder 20. Entropy decoding unit70 of video decoder 30 entropy decodes the bitstream to generatequantized coefficients, motion vectors or intra-prediction modeindicators, and other syntax elements. Entropy decoding unit 70 forwardsthe motion vectors to and other syntax elements to motion compensationunit 72. Video decoder 30 may receive the syntax elements at the videoslice level and/or the video block level.

When the video slice is coded as an intra-coded (I) slice, intraprediction unit 74 may generate prediction data for a video block of thecurrent video slice based on a signaled intra prediction mode and datafrom previously decoded blocks of the current frame or picture. When thevideo frame is coded as an inter-coded (e.g., B, P or GPB) slice, motioncompensation unit 72 produces predictive blocks for a video block of thecurrent video slice based on the motion vectors and other syntaxelements received from entropy decoding unit 70. The predictive blocksmay be produced from one of the reference pictures within one of thereference picture lists. Video decoder 30 may construct the referenceframe lists, List 0 and List 1, using default construction techniquesbased on reference pictures stored in reference frame memory 82. Motioncompensation unit 72 determines prediction information for a video blockof the current video slice by parsing the motion vectors and othersyntax elements, and uses the prediction information to produce thepredictive blocks for the current video block being decoded. Forexample, motion compensation unit 72 uses some of the received syntaxelements to determine a prediction mode (e.g., intra- orinter-prediction) used to code the video blocks of the video slice, aninter-prediction slice type (e.g., B slice, P slice, or GPB slice),construction information for one or more of the reference picture listsfor the slice, motion vectors for each inter-encoded video block of theslice, inter-prediction status for each inter-coded video block of theslice, and other information to decode the video blocks in the currentvideo slice.

Motion compensation unit 72 may also perform interpolation based oninterpolation filters. Motion compensation unit 72 may use interpolationfilters as used by video encoder 20 during encoding of the video blocksto calculate interpolated values for sub-integer pixels of referenceblocks. In this case, motion compensation unit 72 may determine theinterpolation filters used by video encoder 20 from the received syntaxelements and use the interpolation filters to produce predictive blocks.

Video decoder 30 may also include an inter-layer prediction unit 75. Theinter-layer prediction unit 75 is configured to predict a current block(e.g., a current block in the EL) using one or more different layersthat are available in SVC (e.g., a base or reference layer). Suchprediction may be referred to as inter-layer prediction. Inter-layerprediction unit 75 utilizes prediction methods to reduce inter-layerredundancy, thereby improving coding efficiency and reducingcomputational resource requirements. Some examples of inter-layerprediction include inter-layer intra prediction, inter-layer motionprediction, and inter-layer residual prediction. Inter-layer intraprediction uses the reconstruction of co-located blocks in the baselayer to predict the current block in the enhancement layer. Inter-layermotion prediction uses motion information of the base layer to predictmotion in the enhancement layer. Inter-layer residual prediction usesthe residue of the base layer to predict the residue of the enhancementlayer. When the base and enhancement layers have different spatialresolutions, spatial motion vector scaling and/or inter-layer positionmapping may be performed by the inter-layer prediction unit 75 using atemporal scaling function, as described in greater detail below.

Inverse quantization unit 76 inverse quantizes, e.g., de-quantizes, thequantized transform coefficients provided in the bitstream and decodedby entropy decoding unit 70. The inverse quantization process mayinclude use of a quantization parameter QPY calculated by video decoder30 for each video block in the video slice to determine a degree ofquantization and, likewise, a degree of inverse quantization that shouldbe applied.

Inverse transform unit 78 applies an inverse transform, e.g., an inverseDCT, an inverse DST, an inverse integer transform, or a conceptuallysimilar inverse transform process, to the transform coefficients inorder to produce residual blocks in the pixel domain.

After motion compensation unit 72 generates the predictive block for thecurrent video block based on the motion vectors and other syntaxelements, video decoder 30 forms a decoded video block by summing theresidual blocks from inverse transform unit 78 with the correspondingpredictive blocks generated by motion compensation unit 72. Summer 90represents the component or components that perform this summationoperation. If desired, a deblocking filter may also be applied to filterthe decoded blocks in order to remove blockiness artifacts. Other loopfilters (either in the coding loop or after the coding loop) may also beused to smooth pixel transitions, or otherwise improve the videoquality. The decoded video blocks in a given frame or picture are thenstored in reference frame memory 82, which stores reference picturesused for subsequent motion compensation. Reference frame memory 82 alsostores decoded video for later presentation on a display device, such asdisplay device 32 of FIG. 1.

Multi-Layer Decoder

FIG. 3B is a block diagram illustrating an example of a multi-layervideo decoder 31 that may implement techniques in accordance withaspects described in this disclosure. The video decoder 31 may beconfigured to process multi-layer video frames, such as for SHVC andmultiview coding. Further, the video decoder 31 may be configured toperform any or all of the techniques of this disclosure.

The video decoder 31 includes a video decoder 30A and video decoder 30B,each of which may be configured as the video decoder 30 of FIG. 3A andmay perform the functions described above with respect to the videodecoder 30. Further, as indicated by the reuse of reference numbers, thevideo decoders 30A and 30B may include at least some of the systems andsubsystems as the video decoder 30. Although the video decoder 31 isillustrated as including two video decoders 30A and 30B, the videodecoder 31 is not limited as such and may include any number of videodecoder 30 layers. In some embodiments, the video decoder 31 may includea video decoder 30 for each picture or frame in an access unit. Forexample, an access unit that includes five pictures may be processed ordecoded by a video decoder that includes five decoder layers. In someembodiments, the video decoder 31 may include more decoder layers thanframes in an access unit. In some such cases, some of the video decoderlayers may be inactive when processing some access units.

In addition to the video decoders 30A and 30B, the video decoder 31 mayinclude an upsampling unit 92. In some embodiments, the upsampling unit92 may upsample a base layer of a received video frame to create anenhanced layer to be added to the reference picture list for the frameor access unit. This enhanced layer can be stored in the reference framememory 82 (e.g., in its decoded picture buffer, etc.). In someembodiments, the upsampling unit 92 can include some or all of theembodiments described with respect to the resampling unit 90 of FIG. 2A.In some embodiments, the upsampling unit 92 is configured to upsample alayer and reorganize, redefine, modify, or adjust one or more slices tocomply with a set of slice boundary rules and/or raster scan rules. Insome cases, the upsampling unit 92 may be a resampling unit configuredto upsample and/or downsample a layer of a received video frame

The upsampling unit 92 may be configured to receive a picture or frame(or picture information associated with the picture) from the decodedpicture buffer 82 of the lower layer decoder (e.g., the video decoder30A) and to upsample the picture (or the received picture information).This upsampled picture may then be provided to the mode select unit 71of a higher layer decoder (e.g., the video decoder 30B) configured todecode a picture in the same access unit as the lower layer decoder. Insome cases, the higher layer decoder is one layer removed from the lowerlayer decoder. In other cases, there may be one or more higher layerdecoders between the layer 0 decoder and the layer 1 decoder of FIG. 3B.

In some cases, the upsampling unit 92 may be omitted or bypassed. Insuch cases, the picture from the decoded picture buffer 82 of the videodecoder 30A may be provided directly, or at least without being providedto the upsampling unit 92, to the mode select unit 71 of the videodecoder 30B. For example, if video data provided to the video decoder30B and the reference picture from the decoded picture buffer 82 of thevideo decoder 30A are of the same size or resolution, the referencepicture may be provided to the video decoder 30B without upsampling.Further, in some embodiments, the upsampling unit 92 may be a resamplingunit 90 configured to upsample or downsample a reference picturereceived from the decoded picture buffer 82 of the video decoder 30A.

As illustrated in FIG. 3B, the video decoder 31 may further include ademultiplexor 99, or demux. The demux 99 can split an encoded videobitstream into multiple bitstreams with each bitstream output by thedemux 99 being provided to a different video decoder 30A and 30B. Themultiple bitstreams may be created by receiving a bitstream and each ofthe video decoders 30A and 30B receives a portion of the bitstream at agiven time. While in some cases the bits from the bitstream received atthe demux 99 may be alternated one bit at a time between each of thevideo decoders (e.g., video decoders 30A and 30B in the example of FIG.3B), in many cases the bitstream is divided differently. For example,the bitstream may be divided by alternating which video decoder receivesthe bitstream one block at a time. In another example, the bitstream maybe divided by a non-1:1 ratio of blocks to each of the video decoders30A and 30B. For instance, two blocks may be provided to the videodecoder 30B for each block provided to the video decoder 30A. In someembodiments, the division of the bitstream by the demux 99 may bepreprogrammed. In other embodiments, the demux 99 may divide thebitstream based on a control signal received from a system external tothe video decoder 31, such as from a processor on the destination device14. The control signal may be generated based on the resolution orbitrate of a video from the input interface 28, based on a bandwidth ofthe channel 16, based on a subscription associated with a user (e.g., apaid subscription versus a free subscription), or based on any otherfactor for determining a resolution obtainable by the video decoder 31.

Dynamic Range Control of Intermediate Data in Resampling Process

In SHVC, a reference layer picture may need to be resampled, forexample, for interlayer prediction in the enhancement layer. Theresampling can be performed by applying a resampling filter to lumasamples from the reference layer picture. For example, an n-tap filtercan be applied. The resampling process can occur in two steps fortwo-dimensional (2D) resampling. For example, a 2D separableinterpolation filter can be applied. First, horizontal resampling can beperformed on the luma samples, and then, the vertical resampling can beperformed on the luma samples. For example, vertical resampling can beperformed on the video information output from the horizontal resamplingprocess. The resampling filter can receive luma samples as input, andthe horizontal resampling process can generate an intermediate outputbased on the input luma samples. The intermediate output can then beused as the input for the vertical resampling step. In some situations,the horizontal resampling process may add additional bits to the inputluma samples such that the intermediate output has more bits (e.g., hasa greater bit depth) than the input luma samples. The additional bitscan make the data range quite large and may have a significant impact onthe computational complexity of the vertical resampling step. Forexample, the buffer for the intermediate data may be increasedproportionately as data range becomes higher. Also, the complexity ofinterpolation process, especially the multiplication operation, can behighly dependent on the bit-depth of the input data. In addition, thereare certain computational instruction sets that require inputs having abit depth no greater than a certain predetermined maximum. For example,certain 16-bit instruction sets may only be used on inputs having 16bits (e.g., having a 16-bit bit depth).

The filter coefficients can be quantized with 6-bit accuracy, which canbe the same as that of the motion compensation interpolation filter. Inthe 2D separable interpolating process of the early version of SHVC, theoutput of the first interpolating step (e.g., horizontal direction) wasused directly as the input of the second interpolating step (e.g.,vertical direction). The intermediate data between the two dimensioninterpolation steps may extend beyond a certain number of bits, forexample, because additional bits are added from the first interpolatingstep. For example, the first interpolating step can add 8 bits, and theintermediate data between the two dimension interpolation steps may gobeyond 16 bits when the input signal is more than 8 bits. This canincrease the implementation cost of the resampling filter in hardware aswell as software solution. For example, this can increase thecomputational complexity of the resampling filter, especially wheninstruction level parallelism, such as single instruction multiple data(SIMD) instructions, is used. SIMD instructions of most existing CPUscan handle single data with 8 or 16 bit accuracy. Accordingly, it wouldbe advantageous to constrain (e.g., limit or reduce) the bit depth ofthe intermediate output from the horizontal resampling process.

In order to address these and other issues, the techniques described inthis disclosure can constrain the bit depth of the intermediate outputfrom an initial resampling process (e.g., horizontal resampling) to aspecified number of bits. In some embodiments, constraining the bitdepth to a specified number of bits can be accomplished by rightshifting (e.g., applying a right shift operation “>>”) the intermediateoutput by a certain number of bits. The number of bits to right shiftthe intermediate output can be determined based on the bit depth of theinput luma samples to the resampling filter. For example, theintermediate output can be constrained to 16 bits, and the number ofbits to right shift the intermediate output can be calculated bysubtracting 8 bits from the bit depth of the input luma samples. Thenumber of bits shift can be determined dynamically based on the numberof bits of the input luma samples. Constraining the intermediate outputin this way can lead to more accurate results and reduce rounding error,and can allow a coding device and process to take advantage of certainmore efficient coding instruction sets.

In some embodiments, the output from the vertical resampling process canalso be constrained in a similar manner. In certain embodiments, thevertical resampling process can be performed prior to the horizontalresampling process. The techniques can also be applied to a three-stepprocessing case. For example, the three-step process can include a 2Dseparable interpolation process and a color mapping process. In thiscase, the intermediate output from the first step can be constrained toa predetermined bit depth, and the intermediate output of the secondstep can also be constrained to a predetermined bit depth. The number ofbits to shift by can be based on the bit depth of the input luma samplesand/or the bit depth of the intermediate output from the previous step.Generally, the reference layer picture is upsampled, but in someembodiments, the enhancement layer picture may be downsampled.

Certain details relating to the techniques are described below. In someembodiments, the luma sample resampling process or the luma sampleinterpolation process may receive as input:

-   -   the luma reference sample array rlPicSampleL, and    -   a luma sample location (xP, yP) relative to the top-left luma        sample of the current picture,        wherein rlPicSampleL refers to luma sample array of the        reference layer picture and (xP, yP) refers to sample location        of the current pixel which is being processed. Based on the        input, the process can generate as output a resampled luma        sample value rsLumaSample, which refers to the luma sample value        generated by the resampling process. Table 1 specifies one        example of 8-tap filter coefficients f_(L)[p, x] with p=0 . . .        15 and x=0 . . . 7 that may be used for the luma resampling        process.

TABLE 1 16-phase luma resampling filter interpolation filtercoefficients phase p f_(L) [p, 0] f_(L) [p, 1] f_(L) [p, 2] f_(L) [p, 3]f_(L) [p, 4] f_(L) [p, 5] f_(L) [p, 6] f_(L) [p, 7] 0 0 0 0 64 0 0 0 0 10 1 −3 63 4 −2 1 0 2 −1 2 −5 62 8 −3 1 0 3 −1 3 −8 60 13 −4 1 0 4 −1 4−10 58 17 −5 1 0 5 −1 4 −11 52 26 −8 3 −1 6 −1 3 −9 47 31 −10 4 −1 7 −14 −11 45 34 −10 4 −1 8 −1 4 −11 40 40 −11 4 −1 9 −1 4 −10 34 45 −11 4 −110 −1 4 −10 31 47 −9 3 −1 11 −1 3 −8 26 52 −11 4 −1 12 0 1 −5 17 58 −104 −1 13 0 1 −4 13 60 −8 3 −1 14 0 1 −3 8 62 −5 2 −1 15 0 1 −2 4 63 −3 10

In the early versions of the SHVC Working Draft, the value of theresampled luma sample rsLumaSample could be derived by applying thefollowing ordered steps:

-   -   The sample value tempArray[n] with n=0 . . . 7, can derived as        follows:        -   yPosRL=Clip3(0, RefLayerPicHeightlnSamplesL−1, yRef+n−1)        -   refW=RefLayerPicWidthInSamplesL        -   tempArray[n]=            -   (fL[xPhase, 0]*rlPicSampleL[Clip3(0, refW−1, xRef−3),                yPosRL]+fL[xPhase, 1]*rlPicSampleL[Clip3(0, refW−1,                xRef−2), yPosRL]+fL[xPhase, 2]*rlPicSampleL[Clip3(0,                refW−1, xRef−1), yPosRL]+fL[xPhase,                3]*rlPicSampleL[Clip3(0, refW−1, xRef),                yPosRL]+fL[xPhase, 4]*rlPicSampleL[Clip3(0, refW−1,                xRef+1), yPosRL]+fL[xPhase, 5]*rlPicSampleL[Clip3(0,                refW−1, xRef+2), yPosRL]+fL[xPhase,                6]*rlPicSampleL[Clip3(0, refW−1, xRef+3),                yPosRL]+fL[xPhase, 7]*rlPicSampleL[Clip3(0, refW−1,                xRef+4), yPosRL]).    -   The resampled luma sample value rsLumaSample can be derived as        follows:        -   rsLumaSample=            -   (fL[yPhase, 0]*tempArray [0]+fL[yPhase, 1]*tempArray                [1]+fL[yPhase, 2]*tempArray [2]+fL[yPhase, 3]*tempArray                [3]+fL[yPhase, 4]*tempArray [4]+fL[yPhase, 5]*tempArray                [5]+fL[yPhase, 6]*tempArray [6]+fL[yPhase, 7]*tempArray                [7]+(1<<11))>>12        -   rsLumaSample=Clip3(0, (1<<BitDepthY)−1, rsLumaSample),            -   where (xRef, yRef) represents the collocated luma sample                integer pixel position in the reference layer picture,                (xPhase, yPhase) represents the phase of the fractional                sample to be interpolated in horizontal and vertical                directions, and BitDepthY refers to the luma bit depth                of the current picture.

According to certain aspects of the techniques, the value of theresampled luma sample rsLumaSample may be derived by applying thefollowing ordered steps:

-   -   The sample value tempArray[n] with n=0 . . . 7, can derived as        follows:        -   yPosRL=Clip3(0, RefLayerPicHeightlnSamplesL−1, yRef+n−1)        -   refW=RefLayerPicWidthlnSamplesL        -   tempArray[n]=            -   (fL[xPhase, 0]*rlPicSampleL[Clip3(0, refW−1, xRef−3),                yPosRL]+fL[xPhase, 1]*rlPicSampleL[Clip3(0, refW−1,                xRef−2), yPosRL]+fL[xPhase, 2]*rlPicSampleL[Clip3(0,                refW−1, xRef−1), yPosRL]+fL[xPhase,                3]*rlPicSampleL[Clip3(0, refW−1, xRef),                yPosRL]+fL[xPhase, 4]*rlPicSampleL[Clip3(0, refW−1,                xRef+1), yPosRL]+fL[xPhase, 5]*rlPicSampleL[Clip3(0,                refW−1, xRef+2), yPosRL]+fL[xPhase,                6]*rlPicSampleL[Clip3(0, refW−1, xRef+3),                yPosRL]+fL[xPhase, 7]*rlPicSampleL[Clip3(0, refW−1,                xRef+4), yPosRL])>>shift1,            -   where shift1 is defined as: shift1=RefLayerBitDepthY−8,                where RefLayerBitDepthY refers to the luma bit depth of                the reference layer picture.    -   The resampled luma sample value rsLumaSample can be derived as        follows:        -   rsLumaSample=            -   (fL[yPhase, 0]*tempArray[0]+fL[yPhase, 1]*tempArray                [1]+fL[yPhase, 2]*tempArray [2]+fL[yPhase, 3]*tempArray                [3]+fL[yPhase, 4]*tempArray [4]+fL[yPhase, 5]*tempArray                [5]+fL[yPhase, 6]*tempArray [6]+fL[yPhase, 7]*tempArray                [7]+offset>>shift2,            -   where shift2 is defined as:                shift2=12−(BitDepthY−8)=20−BitDepthY, and offset is                defined as: offset=1<<(shift2−1), where BitDepthY refers                to the luma bit depth of the current picture. By                defining shift2 and offset as above, the data range of                the resampled luma sample value can be the same as the                data range of the luma sample of the current picture.        -   rsLumaSample=Clip3(0, (1<<BitDepthY)−1, rsLumaSample),            -   where (xRef, yRef) represents the collocated luma sample                integer pixel position in the reference layer picture                and (xPhase, yPhase) represents the phase of the                fractional sample to be interpolated in horizontal and                vertical directions.

In this manner, the techniques can control the dynamic range ofintermediate data of a 2D separable upsampling filter within 16-bitaccuracy. The right shift bits after the first upsampling step can bedetermined by the bit depth of the input signal. Although 16 bits isused as an example, any number of bits may be selected as appropriatefor bit accuracy.

Certain details relating to the techniques are explained below inreference to FIG. 4 and FIG. 5. Various term used throughout thisdisclosure are broad terms having their ordinary meaning. In addition,in some embodiments, certain terms relate to the following videoconcepts. A picture can refer to video picture as that term is used incurrent standards (e.g., HEVC).

Method for Dynamic Range Control of Intermediate Data in ResamplingProcess

FIG. 4 is a flowchart illustrating an example method for dynamic rangecontrol of intermediate data in resampling process, according to aspectsof this disclosure. The process 400 may be performed by an encoder(e.g., the encoder as shown in FIGS. 2A, 2B, etc.), a decoder (e.g., thedecoder as shown in FIGS. 3A, 3B, etc.), or any other component,depending on the embodiment. The blocks of the process 400 are describedwith respect to the decoder 31 in FIG. 3B, but the process 400 may beperformed by other components, such as an encoder, as mentioned above.The layer 1 video decoder 30B of the decoder 31 and/or the layer 0decoder 30A of the decoder 31 may perform the process 400, depending onthe embodiment. All embodiments described with respect to FIG. 4 may beimplemented separately, or in combination with one another. Certaindetails relating to the process 400 are explained above.

The process 400 starts at block 401. The decoder 31 can include a memory(e.g., reference frame memory 82) for storing video informationassociated with upsampled video information.

At block 402, the decoder 31 obtains video information. For example, thevideo information can include luma samples of the reference layerpicture that is being upsampled. The luma samples can be relative to thetop-left luma sample of the current picture.

At block 403, the decoder 31 upsamples the video information in a firstdimension to generate an intermediate output. In 2D resampling, thefirst dimension can be the horizontal direction.

At block 404, the decoder 31 constrains the intermediate output to apredetermined bit depth. The predetermined bit depth can be selected asappropriate. In one embodiment, the predetermined bit depth can be 16bits. In some embodiments, the decoder 31 can constrain the intermediateoutput to the predetermined bit depth by determining a bit depth of thevideo information, determining a number of bits to shift theintermediate output based upon the bit depth of the video information,and shifting the intermediate output by the number of bits. The decoder31 can shift the intermediate output by the number of bits using a rightshift operation. In one embodiment, the number of bits to shift theintermediate output can be defined as: the bit depth of the videoinformation−8 bits.

In certain embodiments, the decoder 31 determines whether to shift theintermediate output based on the number of bits, and in response todetermining to shift the intermediate output, shifts the intermediateoutput by the number of bits.

At block 405, the decoder 31 upsamples the constrained intermediateoutput in a second dimension, wherein the second dimension is orthogonalto the first dimension. In 2D resampling, the second dimension can bethe vertical direction.

In certain embodiments, the decoder 31 upsamples the constrainedintermediate output to generate a second intermediate output, andconstrains the second intermediate output to a second predetermined bitdepth. For example, the decoder 31 can constrain the second intermediateoutput to the second predetermined bit depth to generate an upsampledversion of the obtained video information. In one embodiment, the secondpredetermined bit depth may be the bit depth of the current enhancementlayer picture. In some embodiments, the decoder 31 can constrain thesecond intermediate output to the second predetermined bit depth bydetermining a second number of bits to shift the second intermediateoutput based upon the bit depth of the video information, and shiftingthe second intermediate output by the second number of bits. The videoinformation may be associated with the reference layer or enhancementlayer, depending on the embodiment. For example, the decoder 31 candetermine the second number of bits to shift the second intermediateoutput based upon the bit depth of the reference layer videoinformation. Or the decoder 31 can determine the second number of bitsto shift the second intermediate output based upon the bit depth of theenhancement layer video information. The decoder 31 can shift the secondintermediate output by the second number of bits using a right shiftoperation. In one embodiment, the second number of bits to shift thesecond intermediate output can be defined as: 20 bits−the bit depth ofthe video information of the enhancement layer.

The decoder 31 can apply a resampling filter to upsample the videoinformation in the first dimension and upsample the constrainedintermediate output in the second dimension.

In certain embodiments, the techniques can apply to 3D videoinformation. For example, the decoder 31 can upsample the constrainedintermediate output to generate a second intermediate output, constrainthe second intermediate output to a second predetermined bit depth, andupsample the constrained second intermediate output in a thirddimension, wherein the third dimension is orthogonal to the firstdimension and the second dimension. The decoder 31 can constrain thesecond intermediate output to the second predetermined bit depth bydetermining a bit depth of the second intermediate output, determine anumber of bits to shift the second intermediate output based upon thebit depth of the second intermediate output, and shift the secondintermediate output by the number of bits. The process 400 ends at block406.

Blocks may be added and/or omitted in the process 400, depending on theembodiment, and blocks of the process 400 may be performed in differentorders, depending on the embodiment. Any features and/or embodimentsdescribed with respect to resampling in this disclosure may beimplemented separately or in any combination thereof. For example, anyfeatures and/or embodiments described in connection with FIG. 4 may beimplemented in any combination with any features and/or embodimentsdescribed in connection with FIG. 5, and vice versa.

FIG. 5 is a flowchart illustrating an example method for dynamic rangecontrol of intermediate data in resampling process, according to aspectsof this disclosure. The process 500 may be performed by an encoder(e.g., the encoder as shown in FIGS. 2A, 2B, etc.), a decoder (e.g., thedecoder as shown in FIGS. 3A, 3B, etc.), or any other component,depending on the embodiment. The blocks of the process 500 are describedwith respect to the decoder 31 in FIG. 3B, but the process 500 may beperformed by other components, such as an encoder, as mentioned above.The layer 1 video decoder 30B of the decoder 31 and/or the layer 0decoder 30A of the decoder 31 may perform the process 500, depending onthe embodiment. All embodiments described with respect to FIG. 5 may beimplemented separately, or in combination with one another. Certaindetails relating to the process 500 are explained above, e.g., withrespect to FIG. 4.

The process 500 starts at block 501. The decoder 31 can include a memory(e.g., reference frame memory 82) for storing video informationassociated with upsampled video information.

At block 502, the decoder 31 obtains video information. For example, thevideo information can include luma samples of the reference layerpicture that is being upsampled. The luma samples can be relative to thetop-left luma sample of the current picture.

At block 503, the decoder 31 upsamples the video information in a firstdimension to generate an intermediate output. In 2D resampling, thefirst dimension can be the horizontal direction.

At block 504, the decoder 31 determines a number of bits to shift theintermediate output based upon the bit depth of the video information.In one embodiment, the number of bits to shift by can be based on 16-bitaccuracy. For example, the intermediate output is shifted so that it canbe limited to a total of 16 bits.

At block 505, the decoder 31 shifts the intermediate output by thenumber of bits. The decoder 31 can shift the intermediate output by thenumber of bits using a right shift operation. As a result, the decoder31 can generate a shifted intermediate output. In one embodiment, thenumber of bits to shift the intermediate output can be defined as: thebit depth of the video information−8 bits.

At block 506, the decoder 31 upsamples the shifted intermediate outputin a second dimension that is orthogonal to the first dimension. In 2Dresampling, the second dimension can be the vertical direction. Theprocess 500 ends at block 507.

Blocks may be added and/or omitted in the process 500, depending on theembodiment, and blocks of the process 500 may be performed in differentorders, depending on the embodiment. Any features and/or embodimentsdescribed with respect to resampling in this disclosure may beimplemented separately or in any combination thereof. For example, anyfeatures and/or embodiments described in connection with FIG. 5 may beimplemented in any combination with any features and/or embodimentsdescribed in connection with FIG. 4, and vice versa.

Terminology

While the above disclosure has described particular embodiments, manyvariations are possible. For example, as mentioned above, the abovetechniques may be applied to 3D video encoding. In some embodiments of3D video, a reference layer (e.g., a base layer) includes videoinformation sufficient to display a first view of a video and theenhancement layer includes additional video information relative to thereference layer such that the reference layer and the enhancement layertogether include video information sufficient to display a second viewof the video. These two views can used to generate a stereoscopic image.As discussed above, motion information from the reference layer can beused to identify additional implicit hypothesis when encoding ordecoding a video unit in the enhancement layer, in accordance withaspects of the disclosure. This can provide greater coding efficiencyfor a 3D video bitstream.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

Information and signals disclosed herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentinvention.

The techniques described herein may be implemented in hardware,software, firmware, or any combination thereof. Such techniques may beimplemented in any of a variety of devices such as general purposescomputers, wireless communication device handsets, or integrated circuitdevices having multiple uses including application in wirelesscommunication device handsets and other devices. Any features describedas modules or components may be implemented together in an integratedlogic device or separately as discrete but interoperable logic devices.If implemented in software, the techniques may be realized at least inpart by a computer-readable data storage medium comprising program codeincluding instructions that, when executed, performs one or more of themethods described above. The computer-readable data storage medium mayform part of a computer program product, which may include packagingmaterials. The computer-readable medium may comprise memory or datastorage media, such as random access memory (RAM) such as synchronousdynamic random access memory (SDRAM), read-only memory (ROM),non-volatile random access memory (NVRAM), electrically erasableprogrammable read-only memory (EEPROM), FLASH memory, magnetic oroptical data storage media, and the like. The techniques additionally,or alternatively, may be realized at least in part by acomputer-readable communication medium that carries or communicatesprogram code in the form of instructions or data structures and that canbe accessed, read, and/or executed by a computer, such as propagatedsignals or waves.

The program code may be executed by a processor, which may include oneor more processors, such as one or more digital signal processors(DSPs), general purpose microprocessors, an application specificintegrated circuits (ASICs), field programmable logic arrays (FPGAs), orother equivalent integrated or discrete logic circuitry. Such aprocessor may be configured to perform any of the techniques describedin this disclosure. A general purpose processor may be a microprocessor;but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration. Accordingly, the term “processor,” as used herein mayrefer to any of the foregoing structure, any combination of theforegoing structure, or any other structure or apparatus suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated software modules or hardware modules configured for encodingand decoding, or incorporated in a combined video encoder-decoder(CODEC).

The coding techniques discussed herein may be embodiment in an examplevideo encoding and decoding system. A system includes a source devicethat provides encoded video data to be decoded at a later time by adestination device. In particular, the source device provides the videodata to destination device via a computer-readable medium. The sourcedevice and the destination device may comprise any of a wide range ofdevices, including desktop computers, notebook (i.e., laptop) computers,tablet computers, set-top boxes, telephone handsets such as so-called“smart” phones, so-called “smart” pads, televisions, cameras, displaydevices, digital media players, video gaming consoles, video streamingdevice, or the like. In some cases, the source device and thedestination device may be equipped for wireless communication.

The destination device may receive the encoded video data to be decodedvia the computer-readable medium. The computer-readable medium maycomprise any type of medium or device capable of moving the encodedvideo data from source device to destination device. In one example,computer-readable medium may comprise a communication medium to enablesource device 12 to transmit encoded video data directly to destinationdevice in real-time. The encoded video data may be modulated accordingto a communication standard, such as a wireless communication protocol,and transmitted to destination device. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device to destination device.

In some examples, encoded data may be output from output interface to astorage device. Similarly, encoded data may be accessed from the storagedevice by input interface. The storage device may include any of avariety of distributed or locally accessed data storage media such as ahard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, the storage device maycorrespond to a file server or another intermediate storage device thatmay store the encoded video generated by source device. Destinationdevice may access stored video data from the storage device viastreaming or download. The file server may be any type of server capableof storing encoded video data and transmitting that encoded video datato the destination device. Example file servers include a web server(e.g., for a website), an FTP server, network attached storage (NAS)devices, or a local disk drive. Destination device may access theencoded video data through any standard data connection, including anInternet connection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., DSL, cable modem, etc.), or acombination of both that is suitable for accessing encoded video datastored on a file server. The transmission of encoded video data from thestorage device may be a streaming transmission, a download transmission,or a combination thereof.

The techniques of this disclosure are not necessarily limited towireless applications or settings. The techniques may be applied tovideo coding in support of any of a variety of multimedia applications,such as over-the-air television broadcasts, cable televisiontransmissions, satellite television transmissions, Internet streamingvideo transmissions, such as dynamic adaptive streaming over HTTP(DASH), digital video that is encoded onto a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some examples, system may be configured to supportone-way or two-way video transmission to support applications such asvideo streaming, video playback, video broadcasting, and/or videotelephony.

In one example the source device includes a video source, a videoencoder, and a output interface. The destination device may include aninput interface, a video decoder, and a display device. The videoencoder of source device may be configured to apply the techniquesdisclosed herein. In other examples, a source device and a destinationdevice may include other components or arrangements. For example, thesource device may receive video data from an external video source, suchas an external camera. Likewise, the destination device may interfacewith an external display device, rather than including an integrateddisplay device.

The example system above merely one example. Techniques for processingvideo data in parallel may be performed by any digital video encodingand/or decoding device. Although generally the techniques of thisdisclosure are performed by a video encoding device, the techniques mayalso be performed by a video encoder/decoder, typically referred to as a“CODEC.” Moreover, the techniques of this disclosure may also beperformed by a video preprocessor. Source device and destination deviceare merely examples of such coding devices in which source devicegenerates coded video data for transmission to destination device. Insome examples, the source and destination devices may operate in asubstantially symmetrical manner such that each of the devices includesvideo encoding and decoding components. Hence, example systems maysupport one-way or two-way video transmission between video devices,e.g., for video streaming, video playback, video broadcasting, or videotelephony.

The video source may include a video capture device, such as a videocamera, a video archive containing previously captured video, and/or avideo feed interface to receive video from a video content provider. Asa further alternative, the video source may generate computergraphics-based data as the source video, or a combination of live video,archived video, and computer-generated video. In some cases, if videosource is a video camera, source device and destination device may formso-called camera phones or video phones. As mentioned above, however,the techniques described in this disclosure may be applicable to videocoding in general, and may be applied to wireless and/or wiredapplications. In each case, the captured, pre-captured, orcomputer-generated video may be encoded by the video encoder. Theencoded video information may then be output by output interface ontothe computer-readable medium.

As noted the computer-readable medium may include transient media, suchas a wireless broadcast or wired network transmission, or storage media(that is, non-transitory storage media), such as a hard disk, flashdrive, compact disc, digital video disc, Blu-ray disc, or othercomputer-readable media. In some examples, a network server (not shown)may receive encoded video data from the source device and provide theencoded video data to the destination device, e.g., via networktransmission. Similarly, a computing device of a medium productionfacility, such as a disc stamping facility, may receive encoded videodata from the source device and produce a disc containing the encodedvideo data. Therefore, the computer-readable medium may be understood toinclude one or more computer-readable media of various forms, in variousexamples.

The input interface of the destination device receives information fromthe computer-readable medium. The information of the computer-readablemedium may include syntax information defined by the video encoder,which is also used by the video decoder, that includes syntax elementsthat describe characteristics and/or processing of blocks and othercoded units, e.g., group of pictures (GOP). A display device displaysthe decoded video data to a user, and may comprise any of a variety ofdisplay devices such as a cathode ray tube (CRT), a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display device. Various embodiments of theinvention have been described. These and other embodiments are withinthe scope of the following claims.

Various embodiments of the invention have been described. These andother embodiments are within the scope of the following claims.

What is claimed is:
 1. An apparatus configured to code videoinformation, the apparatus comprising: a memory configured to storevideo information; and a processor operationally coupled to the memoryand configured to: obtain reference layer video information; upsamplethe reference layer video information in a first dimension to generatean intermediate output; constrain the intermediate output to apredetermined bit depth; and upsample the constrained intermediateoutput in a second dimension, wherein the second dimension is orthogonalto the first dimension.
 2. The apparatus of claim 1, wherein theprocessor is configured to constrain the intermediate output to thepredetermined bit depth by: determining a bit depth of the referencelayer video information; determining a number of bits to shift theintermediate output based upon the bit depth of the reference layervideo information; determining whether to shift the intermediate outputbased on the number of bits; and in response to determining to shift theintermediate output, shifting the intermediate output by the number ofbits.
 3. The apparatus of claim 1, wherein the processor is configuredto constrain the intermediate output to the predetermined bit depth by:determining a bit depth of the reference layer video information;determining a number of bits to shift the intermediate output based uponthe bit depth of the reference layer video information; and shifting theintermediate output by the number of bits.
 4. The apparatus of claim 3,wherein the processor is configured to determine the number of bits toshift the intermediate output as the bit depth of the reference layervideo information minus 8 bits.
 5. The apparatus of claim 3, wherein theprocessor is configured to shift the intermediate output by the numberof bits using a right shift operation.
 6. The apparatus of claim 1,wherein the first dimension is a horizontal dimension and the seconddimension is a vertical dimension.
 7. The apparatus of claim 1, whereinthe reference layer video information comprises luma values.
 8. Theapparatus of claim 1, wherein the processor is configured to upsamplethe reference layer video information in the first dimension andupsample the constrained intermediate output in the second dimension byapplying a resampling filter to the reference layer video information.9. The apparatus of claim 1, wherein the predetermined bit depth is 16bits.
 10. The apparatus of claim 1, wherein the processor is furtherconfigured to: generate a second intermediate output from the upsampled,constrained intermediate output; and constrain the second intermediateoutput to a second predetermined bit depth.
 11. The apparatus of claim10, wherein the processor is further configured to generate an upsampledversion of the obtained reference layer video information from theconstrained second intermediate output.
 12. The apparatus of claim 10,wherein the processor is configured to constrain the second intermediateoutput to the second predetermined bit depth by: determining a secondnumber of bits to shift the second intermediate output based upon thebit depth of the reference layer video information; and shifting thesecond intermediate output by the second number of bits.
 13. Theapparatus of claim 10, wherein the processor is configured to constrainthe second intermediate output to the second predetermined bit depth by:determining a second number of bits to shift the second intermediateoutput based upon the bit depth of enhancement layer video information;and shifting the second intermediate output by the second number ofbits.
 14. The apparatus of claim 13, wherein the processor is configuredto shift the second intermediate output by the second number of bitsusing a right shift operation.
 15. The apparatus of claim 13, whereinthe processor is further configured to determine the second number ofbits to shift the second intermediate output as: 20 bits minus the bitdepth of the enhancement layer video information.
 16. The apparatus ofclaim 1, wherein the apparatus is selected from a group consisting ofone or more of: a desktop computer, a notebook computer, a laptopcomputer, a tablet computer, a set-top box, a telephone handset, a smartphone, a smart pad, a television, a camera, a display device, a digitalmedia player, a video gaming console, and a video streaming device. 17.A method of coding video information, the method comprising: obtainingreference layer video information; upsampling the reference layer videoinformation in a first dimension to generate an intermediate output;constraining the intermediate output to a predetermined bit depth; andupsampling the constrained intermediate output in a second dimension,wherein the second dimension is orthogonal to the first dimension. 18.The method of claim 17, wherein said constraining the intermediateoutput to the predetermined bit depth comprises: determining a bit depthof the reference layer video information; determining a number of bitsto shift the intermediate output based upon the bit depth of thereference layer video information; determining whether to shift theintermediate output based on the number of bits; and in response todetermining to shift the intermediate output, shifting the intermediateoutput by the number of bits.
 19. The method of claim 17, wherein saidconstraining the intermediate output to the predetermined bit depthcomprises: determining a bit depth of the reference layer videoinformation; determining a number of bits to shift the intermediateoutput based upon the bit depth of the reference layer videoinformation; and shifting the intermediate output by the number of bits.20. The method of claim 19, wherein the number of bits to shift theintermediate output is determined as the bit depth of the referencelayer video information minus 8 bits.
 21. The method of claim 19,wherein said shifting the intermediate output by the number of bits isperformed using a right shift operation.
 22. The method of claim 17,wherein the first dimension is a horizontal dimension and the seconddimension is a vertical dimension.
 23. The method of claim 17, whereinthe reference layer video information comprises luma values.
 24. Themethod of claim 17, wherein said upsampling the reference layer videoinformation in the first dimension and said upsampling the constrainedintermediate output in the second dimension are performed by applying aresampling filter to the reference layer video information.
 25. Themethod of claim 17, wherein the predetermined bit depth is 16 bits. 26.The method of claim 17, further comprising: generating a secondintermediate output from the upsampled, constrained intermediate output;and constraining the second intermediate output to a secondpredetermined bit depth.
 27. The method of claim 26, further comprisinggenerating an upsampled version of the obtained reference layer videoinformation from the constrained second intermediate output.
 28. Themethod of claim 26, wherein said constraining the second intermediateoutput to the second predetermined bit depth comprises: determining asecond number of bits to shift the second intermediate output based uponthe bit depth of the reference layer video information; and shifting thesecond intermediate output by the second number of bits.
 29. The methodof claim 26, wherein said constraining the second intermediate output tothe second predetermined bit depth comprises: determining a secondnumber of bits to shift the second intermediate output based upon thebit depth of enhancement layer video information; and shifting thesecond intermediate output by the second number of bits.
 30. The methodof claim 29, wherein said shifting the second intermediate output by thesecond number of bits is performed using a right shift operation. 31.The method of claim 29, wherein the second number of bits to shift thesecond intermediate output is determined as: 20 bits minus the bit depthof the enhancement layer video information.
 32. A non-transitorycomputer readable medium comprising instructions that when executed on aprocessor comprising computer hardware cause the processor to: storevideo information; obtain reference layer video information; upsamplethe reference layer video information in a first dimension to generatean intermediate output; constrain the intermediate output to apredetermined bit depth; and upsample the constrained intermediateoutput in a second dimension, wherein the second dimension is orthogonalto the first dimension.
 33. The computer readable medium of claim 32,further comprising instructions to cause the processor to constrain theintermediate output to the predetermined bit depth by: determining a bitdepth of the reference layer video information; determining a number ofbits to shift the intermediate output based upon the bit depth of thereference layer video information; and shifting the intermediate outputby the number of bits.
 34. An apparatus configured to code videoinformation, the apparatus comprising: means for storing videoinformation; means for obtaining reference layer video information;means for upsampling the reference layer video information in a firstdimension to generate an intermediate output; means for constraining theintermediate output to a predetermined bit depth; and means forupsampling the constrained intermediate output in a second dimension,wherein the second dimension is orthogonal to the first dimension. 35.The apparatus of claim 34, wherein the means for constraining theintermediate output to the predetermined bit depth is configured toconstrain the intermediate output to the predetermined bit depth by:determining a bit depth of the reference layer video information;determining a number of bits to shift the intermediate output based uponthe bit depth of the reference layer video information; and shifting theintermediate output by the number of bits.